This application is related to Japanese Patent Application No. 2001-109,379, filed Apr. 9, 2001, which application is hereby incorporated by reference in its entirety.
1. Field of the Invention
The present invention generally relates to engine mounts used on small vehicles. More particularly, the present invention relates to an engine mounting arrangement that improves the rigidity of the connection between the engine and the vehicle while reducing the transmission of vibrations between the engine and the vehicle.
2. Description of the Related Art
All terrain vehicles are a smaller type of vehicle that generally are used for both recreation and utilitarian purposes. In either application, the vehicles are frequently driven over rough terrain in areas in which roads do not exist. As such, operators of the vehicles are subject to a variety of jolts and impacts incurred during operation.
In many all terrain vehicles, four wheels are suspended from a frame assembly. These four wheels are connected to an engine such that the vehicle can be driven in two-wheel or four-wheel drive modes. In some all terrain vehicles, the wheels and the engine are coupled by a shaft drive assembly. In other all terrain vehicles, the wheels and the engine are coupled by a flexible loop, such as a drive belt or chain.
During operation, the engine and the drive train are subject to a variety of forces. For instance, during rapid acceleration of the engine, the rapid increase in crankshaft speed causes the balance of the engine to produce a reaction force. The reaction force is counter to the direction of crankshaft rotation. In addition, simple running of the engine causes a variety of vibrations, as is known in the art.
To counter the reaction force, engine mounts can be made of a stiff material such that the forces created during rapid speed increases are adequately resisted by the engine mounts. Such a construction reduces movement of the engine relative to the frame; however, such a construction increases the amount of vibrations transmitted to the frame. It has been found that movement of the engine resulting from reaction forces tends to rotate the engine about the crankshaft axis while operation of the vehicle and the engine result in oscillations about axes normal to the crankshaft axis.
Various attempts have been made to counter these forces. U.S. Pat. No. 3,811,528, issued to Hooper, exemplified some of these attempts. Hooper described a technique to that was used to mount a 180 degree twin engine. These engines have certain complications in attenuating vibration energy because the engines have two cylinders operating in the same plane with a phase difference of 180 degrees. Thus, the engine operation is accompanied by forces that are coupled, which forces cause an oscillation of the engine. Hooper determined that placing engine mountings at a particular location could balance the stiffness moments. The engine mountings were disclosed to be stiffer in an axial direction than in circumferential directions about the axis of oscillation.
Even the construction in Hooper, however, failed to adequately compensate for the diverse forces and vibrations set up by operation of the engine. Hooper""s engine mounts provided increased damping in shear and increased support in compression; however, Hooper""s triangulated mount placement was difficult for manufacturing reasons and failed to adequately support the engine unit. Accordingly, an improved engine mounting arrangement is desired.
One aspect of the present invention involves a small vehicle comprising a frame assembly with at least one wheel supporting the frame assembly. The frame assembly comprises a pair of bottom rails that are laterally spaced from each other and a transverse generally horizontal plane extending through a centerline of each of the bottom rails. An engine compartment is defined above the transverse generally horizontal plane. An engine is disposed within the frame assembly with the engine being drivingly connected to the at least one wheel. The engine comprises a crankshaft having an axis of rotation and a center of gravity. The engine further comprises a first mounting side and a second mounting side. The first mounting side and the second mounting side extend generally parallel to the axis of crankshaft rotation. A first engine mount and a second engine mount are spaced from each other and are secured to the first mounting side of the engine. A third engine mount and a fourth engine mount are spaced from each other and are secured to the second mounting side of the engine. Each of the first engine mount, the second engine mount, the third engine mount and the fourth engine mount comprises a pair of plates that are spaced by a resilient material. The resilient material is more compliant in a shear direction than in a direction normal to the shear direction. A first plane is defined through the direction normal to the shear direction of the first engine mount and the first mounting side. A second plane is defined through the direction normal to the shear direction of the second engine mount and the second mounting side. The first plane and the second plane intersect at the center of gravity.
Another aspect of the present invention involves a small vehicle comprising a frame assembly with an engine mounted to the frame assembly. The engine comprises a transversely extending crankshaft. A front engine mount is disposed between the engine and the frame assembly and a rear engine mount is disposed between the engine and the frame assembly. The front engine mount and the rear engine mount both comprise a pair of plates that are separated by a block of elastomeric material. The block of elastomeric material is seven times stiffer in compression than in shear. The front engine mount is disposed on a first imaginary transverse cylinder centered at a center of gravity of the engine and the rear engine mount is disposed on a second imaginary transverse cylinder centered at the center of gravity of the engine. The front engine mount has a shear direction that is tangential to the first cylinder and a compression direction that is normal to the shear direction while the rear engine mount has a shear direction that is tangential to the second cylinder and a compression direction that is normal to the shear direction such that a compression direction of each engine mount extends through a transverse axis intersecting the center of gravity.
A further aspect of the present invention involves a small vehicle comprising a frame assembly with an engine mounted to the frame assembly. The engine comprises a transversely extending crankshaft. A first pair of engine mounts and a second pair of engine mounts are disposed between the engine and the frame assembly. The first pair of engine mounts comprises a first front engine mount and a first rear engine mount and the second pair of engine mounts comprises a second front engine mount and a second rear engine mount. Each of the engine mounts comprises a pair of plates that are separated by a block of elastomeric material. The block of elastomeric material is seven times stiffer in compression than in shear. The first pair of engine mounts and the second pair of engine mounts being laterally separated by a longitudinally extending center plane that substantially bisects the vehicle. The first pair of engine mounts is disposed on a pair of hypothetical cylinders centered along an axis extending through a center of gravity of the engine in a direction parallel to an axis of crankshaft rotation and the second pair of engine mounts also is disposed on the pair of hypothetical cylinders.